1. Field of the Invention
The present invention relates to a crimped electric wire with a terminal and a method for producing the same.
2. Description of the Related Art
Generally, a terminal fitting equipped with an electric wire crimping section for crimping a core wire exposed at the end of an electric wire is known as a terminal fitting that is connected to the end of an electric wire. This electric wire crimping section has a pair of barrel pieces rising from both end fringes of the bottom plate of the terminal fitting. When the core wire is placed on the bottom plate and swaged using an anvil and a crimper in the vertical direction, the core wire is conductively connected to the electric wire crimping section.
The issue of specifically determining what kind of shape is formed as the crimped shape of the core wire using the barrel pieces of the electric wire crimping section is generally controlled depending on the value of the crimp height (the height dimension of the electric wire crimping section) in a crimping machine. Although the crimp width (the width dimension of the electric wire crimping section) is available as a parameter for determining the shape of the electric wire crimping section, the crimp width is determined, for example, by the dimensions of the cavity in a connector housing accommodating the terminal fitting and the value of the crimp width is settled to a specific value depending on the shapes of the anvil and the crimper. Hence, only the downward stroke (this determines the crimp height) of the crimper of the crimping machine toward the anvil can be adjusted at the time of the crimping.
Conventionally, in the case that a copper electric wire having a core wire made of copper or copper alloy (hereafter simply referred to as “copper”) is crimped, the crimp height is generally adjusted so that the core wire is crimped at a relatively low compression ratio (at a compression ratio lower than that in the case that an aluminum electric wire is crimped as described below).
However, in recent years, for the purpose of making electric wires lighter and using alternate electric wires instead of copper electric wires, a study of using aluminum electric wires having a core wire made of aluminum or aluminum alloy (hereafter simply referred to as “aluminum”) for vehicle wire harnesses is being conducted. Aluminum has properties such that the rigidity of aluminum is higher than that of copper and such that a non-conductive film is apt to be formed on the surface of aluminum. Hence, it is assumed that an aluminum electric wire should be crimped at a compression ratio higher than that when a copper electric wire is crimped. By virtue of the high compression crimping, the non-conductive film is easily broken, and the contact resistance can be prevented from increasing even when the terminal fitting is subjected to a thermal shock cycle.
However, copper alloy or brass is generally used as the base material of the terminal fitting although the aluminum electric wire is made of aluminum. Hence, when high compression crimping is performed, a problem is revealed in which the elongation of the electric wire crimping section is larger than that in the case of the copper electric wire. Accordingly, for the purpose of suppressing the elongation ratio of the electric wire crimping section due to the high compression crimping, attempts to solve this problem have been made by using methods in which the terminal fitting is made of an expensive material having a small elongation ratio and the shape of the terminal fitting is modified ingeniously, for example.
Since high compression is required in the case of crimping the aluminum electric wire as described above, the elongation ratio of the terminal fitting inevitably becomes large. On the other hand, if the compression ratio is relieved, the contact resistance increases when the terminal fitting is subjected to a thermal shock cycle, whereby the compression ratio cannot be relieved. For these reasons, it has been considered very difficult to simultaneously suppress the elongation ratio of the terminal fitting and suppress the contact resistance from increasing as long as the aluminum electric wire is crimped.
Besides, the above related arts are disclosed by JP-A-H07-73950 and JP-A-2006-12716.